The synthesis, structures and reactions of zinc and cobalt metal–organic frameworks incorporating an alkyne-based dicarboxylate linker

The reaction of zinc(ii) nitrate and 4,4[prime or minute]-ethynylenedibenzoic acid (H2edb) in DMF at 80 [degree]C gave the metal-organic framework material [Zn4O(edb)3(H2O)2][middle dot]6DMF 1 in which edb ligands connect Zn4O centres into a doubly-interpenetrated cubic network with a similar topology to observed with other linear dicarboxylates in the IRMOF series. Analysis of the nitrogen isotherm revealed the material to have a BET surface area of 1088 m2 g-1, which is approximately one-third of the value calculated from GCMC simulations, suggesting incomplete activation or pore blocking in the activated material. The reaction of cobalt(ii) nitrate and H2edb in DMF gave [Co3(edb)3(DMF)4][middle dot]2.6DMF 2. The structure of 2 is based on Co3(O2CR)6 linear secondary building units that are linked by the edb ligands into a two-dimensional network. When 2 was placed under vacuum, a colour change from pale pink to deep blue was observed, which is consistent with loss of the coordinated DMF molecules. When treated with [Co2(CO)8], crystals of 1 turned dark red, and IR analysis is consistent with coordination of Co2(CO)6 fragments to the alkyne groups. However, the colour change was restricted to the external crystal surfaces. This is a likely consequence of partial framework collapse, which occurs following coordination of Co2(CO)6 to the alkyne groups. Coordination changes the preferred angle between carboxylate groups in the edb ligand, which in turn introduces strain into the network.